We previously demonstrated that overexpression of protein kinase C (PKC)-alpha and -delta enables phorbol esters (TPA) to induce monocytic differentiation of 32D myeloid progenitor cells, and that PKC-delta becomes tyrosine phosphorylated in response to TPA and platelet-derived growth factor (PDGF) stimulation. While tyrosine 187 was demonstrated to be a major PKC-delta phosphorylation site, mutation of this site did not detectable affect PKC-delta enzymatic activity. Therefore, we are attempting to define and mutate tyrosine phosphorylation sites in order to fully determine if this type of phosphorylation impinges on its enzymatic activity. However, our recent study has demonstrated that serine 643 is an important autophosphorylation site that positively affects PKC-delta enzymatic activity. - Cancer cell growth regulation, cell proliferation, Cell signaling, Differentiation, macrophages, protein function, Protein Kinase, protein phosphorylation, receptors, - Human Tissues, Fluids, Cells, etc.